CS 157B: Database Management Systems II February 6 Class Meeting Department of Computer Science San Jose State University Spring 2013 Instructor: Ron Mak

Department of Computer Science Spring 2013: February 6 CS 157B: Database Management Systems II © R. Mak 2 Hibernate Oral Presentations  Next Monday, February 11.  Four teams volunteer to each give a quick 15-minute presentation and demo of its project. What data did you use. Logical design of your database. How you used Hibernate. Demo of your application. Q & A

Department of Computer Science Spring 2013: February 6 CS 157B: Database Management Systems II © R. Mak 3 Hibernate Oral Presentations  Monday, February 11  Section 1 Team Cosmos Team VoidStarStar  Section 2 Team Xeon

Department of Computer Science Spring 2013: February 6 CS 157B: Database Management Systems II © R. Mak 4 Internet Connection Required  Recall the configuration file hibernate.cfg.xml :  The URL is for the Document Type Definition (DTD). Hibernate can’t parse the configuration file without it. Therefore, you need a working Internet connection to execute a Hibernate program! <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "

Department of Computer Science Spring 2013: February 6 CS 157B: Database Management Systems II © R. Mak 5 No Internet Connection Required  Solution: Download that DTD and put it somewhere local, such as in your source folder. Modify your hibernate.cfg.xml accordingly: <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "file:///G:/NetBeansProjects/SchoolDemo5/src/hibernate-configuration-3.0.dtd">...

Department of Computer Science Spring 2013: February 6 CS 157B: Database Management Systems II © R. Mak 6 Queries Without SQL ... or anything that resembles SQL.  Hibernate offers an object-oriented way to formulate and execute database queries.  Criteria API Build nested, structured query expressions in Java. Compile-time syntax checking.  Unlike embedded SQL. Like Hibernate itself, it isn’t perfect.

Department of Computer Science Spring 2013: February 6 CS 157B: Database Management Systems II © R. Mak 7 Get a List of Objects of a Class  Sort them: Session session = HibernateContext.getSession(); Criteria criteria = session.createCriteria(Student.class); List students = (List ) criteria.list(); criteria.addOrder(Order.asc("lastName")); List students = criteria.list();  Paginate: Get only the first 5 objects. criteria.setFirstResult(0); criteria.setMaxResults(5); List students = (List ) criteria.list(); Also: Order.desc()

Department of Computer Science Spring 2013: February 6 CS 157B: Database Management Systems II © R. Mak 8 Query by Example  Query by Example (QBE) is a simple query technique. Create a prototype object. Set one or more of the prototype object’s field values. Use the prototype object to make an example object. Use the example object in a query to fetch all the objects whose field values match those of the example. Student prototype = new Student(); prototype.setLastName("Smith"); Example example = Example.create(prototype); Session session = HibernateContext.getSession(); Criteria criteria = session.createCriteria(Student.class); criteria.add(example); Student student = (Student) criteria.uniqueResult(); QBE doesn’t seem to work with the primary key field.

Department of Computer Science Spring 2013: February 6 CS 157B: Database Management Systems II © R. Mak 9 Query by Example  Ignore zero-valued fields when matching: Example example = Example.create(... ); example.excludeZeroes();  Don’t ignore null fields. The default is to ignore null fields when matching. Also enables matching on zero-valued fields. Example example = Example.create(... ); example.excludeNone();  Ignore a particular field: Example example = Example.create(... ); example.excludeProperty("firstName");

Department of Computer Science Spring 2013: February 6 CS 157B: Database Management Systems II © R. Mak 10 Query by Example  Fuzzy matches: Get all students whose addresses end in.com  MatchMode ANYWHERE START END EXACT Student prototype = new Student(); prototype.set Address(".com"); Example example = Example.create(prototype); example.enableLike(MatchMode.END); Session session = HibernateContext.getSession(); Criteria criteria = session.createCriteria(Student.class); criteria.add(example); List students = (Student) criteria.list();

Department of Computer Science Spring 2013: February 6 CS 157B: Database Management Systems II © R. Mak 11 Restrictions  Query by example has some obvious limitations. What about the query “fetch all students with GPA > 3.0”?  Use the Criteria API’s Restrictions class. This class has many static methods. See: Session session = HibernateContext.getSession(); Criteria criteria = session.createCriteria(Student.class); criteria.add(Restrictions.gt("gpa", 3.0f)); List smarties = (List ) criteria.list();

Department of Computer Science Spring 2013: February 6 CS 157B: Database Management Systems II © R. Mak 12 Restrictions  You can “and” together multiple restrictions: Criterion crit1 = Restrictions.gt("gpa", 3.0f); Criterion crit2 = Restrictions.le("gpa", 3.5f); Criterion crit3 = Restrictions.isNotNull(" Address"); Student prototype = new Student(); prototype.set Address(".com"); Example example = Example.create(prototype); example.enableLike(MatchMode.END); example.ignoreCase(); Session session = HibernateContext.getSession(); Criteria criteria = session.createCriteria(Student.class); criteria.add(crit1); criteria.add(crit3); criteria.add(example); List students = (List ) criteria.list();

Department of Computer Science Spring 2013: February 6 CS 157B: Database Management Systems II © R. Mak 13 Restrictions  You can also “or” together multiple restrictions. Fetch all students whose GPA is less that 3.0 or greater than 3.5 Criterion crit1 = Restrictions.lt("gpa", 3.0f); Criterion crit2 = Restrictions.gt("gpa", 3.5f); Disjunction disjunction = Restrictions.disjunction(); disjunction.add(crit1); disjunction.add(crit2); Session session = HibernateContext.getSession(); Criteria criteria = session.createCriteria(Student.class); criteria.add(disjunction); List students = (List ) criteria.list();

Department of Computer Science Spring 2013: February 6 CS 157B: Database Management Systems II © R. Mak 14 Criteria and Associations  What classes are taught by John Lane? Sorted by subject.  “Chain” criteria across associated objects. Use the reference fields. IdLastFirst 7003RogersTom 7008ThompsonArt 7012LaneJohn 7051FlynnMabel CodeTeacher_idSubject Data structures Java programming Compilers Software engineering Operating systems TeacherClass

Department of Computer Science Spring 2013: February 6 CS 157B: Database Management Systems II © R. Mak public class Klass {... private public Teacher getTeacher() { return teacher; } public void setTeacher(Teacher teacher) { this.teacher = teacher; }... }  What classes are taught by John Lane?

Department of Computer Science Spring 2013: February 6 CS 157B: Database Management Systems II © R. Mak 16 Criteria and Associations IdLastFirst 7003RogersTom 7008ThompsonArt 7012LaneJohn 7051FlynnMabel CodeTeacher_idSubject Data structures Java programming Compilers Software engineering Operating systems TeacherClass Session session = HibernateContext.getSession(); Criteria classCriteria = session.createCriteria(Klass.class); Criteria teacherCriteria = classCriteria.createCriteria("teacher"); teacherCriteria.add(Restrictions.eq("firstName", "John")).add(Restrictions.eq("lastName", "Lane")); classCriteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY); classCriteria.addOrder(Order.asc("subject")); List klasses = (List ) classCriteria.list();

Department of Computer Science Spring 2013: February 6 CS 157B: Database Management Systems II © R. Mak 17 public class Student {... private List klasses = new public List getKlasses() { return klasses; } public void setKlasses(List klasses) { this.klasses = klasses; }... }  Who are the students taught by John Lane?

Department of Computer Science Spring 2013: February 6 CS 157B: Database Management Systems II © R. Mak 18 Criteria and Associations  Who are the students taught by John Lane? Session session = HibernateContext.getSession(); Criteria studentCriteria = session.createCriteria(Student.class); Criteria classCriteria = studentCriteria.createCriteria("klasses"); Criteria teacherCriteria = classCriteria.createCriteria("teacher"); teacherCriteria.add(Restrictions.eq("firstName", "John")).add(Restrictions.eq("lastName", "Lane")); studentCriteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY); studentCriteria.addOrder(Order.asc("lastName")); List students = (List ) studentCriteria.list(); SchoolDemo6 Why is this line necessary?

Department of Computer Science Spring 2013: February 6 CS 157B: Database Management Systems II © R. Mak 19 Project #1  Now you should be able to use Hibernate to: Map Java classes to relational database tables. Specify one-to-one, one-to-many, and many-to- many associations, and handle class hierarchies. Create and populate your database tables.  Use sample datasets downloaded from the Internet, or make up your own data. Do queries using the Criteria API. _

Department of Computer Science Spring 2013: February 6 CS 157B: Database Management Systems II © R. Mak 20 Hibernate Query Language (HQL)  Looks like SQL.  However, queries are based on Java classes and their fields, not database tables. Insulate your Java code from the database.  Value injection with named parameters.  Example: public static Teacher find(String lastName) { Session session = HibernateContext.getSession(); Query query = session.createQuery("from Teacher where lastName = :name"); query.setString("name", lastName); Teacher teacher = (Teacher) query.uniqueResult(); session.close(); return teacher; }

Department of Computer Science Spring 2013: February 6 CS 157B: Database Management Systems II © R. Mak 21 Native SQL  As a last resort, Hibernate allows native SQL.  Example: The result will be an array of field values.  Similar to a JDBC result set. Session session = HibernateContext.getSession(); SQLQuery query = session.createSQLQuery( "SELECT * FROM Teacher WHERE last_name = '" + lastName + "'"); Object result = query.uniqueResult();